This invention relates to a method and composition for reducing fouling and sliming of submerged objects and marine structures for extended periods of time.
The fouling of boat hulls and other objects immersed in sea water is a well-known problem. Fouling is a term used to describe the damage caused by the growth of certain marine macro-organisms such as barnacles, mollusks, incrusting bryozoans, annelids, hydroides, algae, etc. It is well-known that these organisms are highly susceptible to copper. Accordingly, for centuries sailing vessels have been clad with copper hulls. More recently copper has been applied to hulls in the form of paints, polymers, or copper containing polymers.
Perhaps the most common method of preventing the fouling of a boat hull, particularly on small crafts, is the use of anti-fouling paints. Such paints are applied to all surfaces of the hull exposed to water for any prolonged period of time. Indeed, even fiberglass hulls, which otherwise do not require painting, are normally painted at the beginning of each boating season with an anti-fouling paint on areas of the hull which will become exposed to water for long periods of time during the boating season. It would, of course, be highly desirable to provide a gel coat for fiberglass hulls which is anti-fouling for several years. The polymeric composition of the present invention can be utilized as such a gel coat.
In addition to being anti-fouling, the gel coat composition of the present invention also exhibits resistance to sliming. Sliming is a term used to describe the opaque film which forms on the surface of submerged objects. Sliming is generally caused by micro-organisms such as bacteria. Indeed, when a vessel is placed in salt water, initially bacteria becomes associated with the surface of the object to form a film of slime. The association of the bacteria is followed by an association of a biotic progression of diatoms, hybrides, algae, bryozoans, protozoans, and finally macro-organisms (foulents). It is desirable to reduce sliming for many reasons. Obviously, the presence of slime contributes to problems associated with foulents such as increasing drag, increasing fuel consumption, etc. However, perhaps more significant is the fact that macro-organisms tend to be rugophilic and settle on roughened surfaces in preference to smooth surfaces. Thus, there is a view that marine slimes precondition the surface of submerged objects in a manner that stimulates the settling of foulents. Thus, slime provides the physical substrate and possibly a nutriant source which encourages the attachment of macroscopic plants and animals. Obviously, it would be desirable to provide a material which not only prevents fouling but which also reduces sliming. This fact is significant because anti-fouling paints are not generally characterized as being anti-sliming. The conventional method of preventing sliming is to chemical treat the water, i.e., chlorination or ozonation.
Of course, fouling and sliming is also a problem which occurs when objects are in contact with fresh water. Thus, the gel coat of the present invention can be used to coat objects which remain in contact with fresh water for prolonged periods of time.
As has been stated above, a common procedure for preventing a boat hull from fouling is to apply an anti-fouling paint. Typically, an anti-fouling paint contains an anti-fouling metal such as copper which leaches into the water to form copper ions. These ions are deadly to the foulents. As one particle of the anti-fouling metal dissolves, another particular is exposed to solvolysis. This leaching is rapid (when compared to the leaching rate of solid copper) and varies with such factors as coating age, temperature of the water, salinity of the water, etc.
Quantitive information indicates that in most cases, initially the leaching rate of anti-fouling paints is excessive and results in overkill. Furthermore, the rapid leaching leads to the concentration of the toxic metallic components in quantities well above that normally present in the ocean. Of course, the longer the object to which the anti-fouling paint has been applied is in the water, the less metallic material is available to prevent fouling.
Copper cladding on the other hand leaches copper ions very slowly. However, this slow leaching is still effective in killing foulents. Furthermore, copper cladding is effective as an anti-foulent for many years. Indeed, it can be stated that anti-foulents that leach slowly last longer. It would be highly desirable to provide an anti-fouling gel coat material which has a slow leach rate. The gel coat of the present invention is such a material.